Electrophoresis Of Suspensions Research Articles

Gel electrophoresis in suspensions of charged spherical particles

Gel-electrophoresis, the migration of colloidal particles through a polymer gel in response to an applied electric field, is investigated theoretically in this study. It is a very powerful technique widely used in soft matter science. Both the short range steric effect (due to the direct contact friction between the gel and the migrating particles) and the long range hydrodynamic effect (due to the hydrodynamic force of the gel exerted upon the liquid suspension) are considered with the particle mobility calculated as the product of the predictions from these two approaches separately. Brinkman fluid is assumed to model the polymer gel and Kuwabara's unit cell model is employed to represent the suspension of particles. A pseudo-spectral method is adopted to solve the resulting general electrokinetic equations. We find, among other things, that the deformation of ion clouds surrounding the particles due to the convection flow within the porous gels deters the particle motion significantly, as an induced electric field opposite to the applied electric field is generated, an effect referred to as the polarization effect here. The higher the surface potential of the particle is, the more significant the reduction of mobility due to this polarization effect. Local extrema are observed in the mobility profiles with varying double layer thickness around κa = 1, where κ is the reciprocal of Debye length, and a is the particle radius, as the polarization effect manifests itself there in general. The presence of the gel retards the particle motion in general. The poorer the permeability is, the more severe the reduction. On the other hand, the more concentrated the particle suspension is, the slower the particle motion in general, due to the hindrance effect between neighboring particles. Moreover, the involvement of polarization and overlapping effects of the double layer further complicates the electrophoretic behavior of the particle, which is discussed in detail. Excellent agreement is obtained between the results reported here and the experimental data available in the literature for gold nanoparticles in dilute suspensions. The current study greatly extends the theoretical analysis scope of gel-electrophoresis from previous dilute suspensions only to concentrated ones as well, which are encountered frequently in practical applications in biological and biochemical fields, as well as other fields involving soft matters such as colloids and polymer gels.

Electrophoresis in suspensions of charged porous spheres in salt-free media

Electrophoresis in either dilute or concentrated suspensions of charged porous spheres in salt-free media is investigated theoretically in this study. The Brinkman model and the Kuwabara’s unit cell model are adopted to simulate the porous structure and the suspensions, respectively. We found, among other things, that the polarization effect due to the convection flow within the porous sphere is a crucial factor in determining its electrophoretic behavior. An induced electric field opposite to the applied electric field is generated, which deters the particle motion significantly when the particle is highly permeable. Approximate analytical prediction for dilute suspensions neglecting convection flow can overestimate the mobility severely in this situation. The approximate analytical prediction is satisfactory when the permeability of particle is low, though. Counterion condensation happens at high fixed charge density which decreases the mobility drastically and the mobility approaches a constant value asymptotically. The mobility profile of the particles with increasing volume fraction can exhibit local minimum if the corresponding dimensionless parameter Q fix /( λa) 2 is high, where Q fix and λa are, respectively, the fixed charge density and the friction coefficient of the porous particles in dimensionless form. This is due to the overlapping of counterion clouds surrounding particles, which offsets the polarization effect, becomes significant as the suspension gets concentrated. No such phenomenon for low Q fix /( λa) 2, where the mobility profile decreases monotonously with increasing volume fraction. Comparison with experimental data available in the literature for polyelectrolyte suspensions is excellent, indicating the reliability of this analysis, as well as the success of using charged porous sphere to model a polyelectrolyte system.

Deposition of YBa 2Cu 3O 7−δ over metallic substrates by electrophoresis of suspensions in isobutylmethylketone. Influence of electric field, thermal and mechanical treatments

Superconducting YBa 2Cu 3O 7−δ coatings have been prepared over metallic wires, plates and other complex shape articles by electrophoresis of suspensions in isobutylmethylketone. Further annealing in a controlled atmosphere and the chemical identity of the metallic substrate are determinant parameters influencing the superconducting properties observed. Silver metal is the least reactive substrate and the one where deposits with the best properties have been obtained. Ag diffuses into the coating to a large extent acting as a cement among oxide particles. Sintering efforts have been carried out using various oxygen partial pressures including those for which the YBa 2Cu 3O 7−δ peritectic point lies close to the melting point of silver. Preferential orientation has been observed and evaluated by X-ray diffraction. The wires obtained show high T c values ( T c=92 K) and narrow transitions in their susceptibility and resistivity curves when their thermal treatment is done in oxygen or air. The J c values observed are high, maximum values of 4500 A/cm 2 (liquid N 2) and 19400 A/cm 2 (liquid He), as compared with previously reported values for articles prepared by the same method.

Thermo-osmosis and electro-osmosis of water and electrophoresis of suspensions in water

Experimental studies on the thermo-osmosis, electro-osmosis and electrophoresis of water carried out by the authors are reviewed. The flow rate of water through swollen cellophane membranes is found to depend on temperature difference in a linear manner up to Δ T = 25°C. Thermo-osmosis occurs only if the pore size of the membrane is greater than the molecular diameter and is comparable with the mean free path of the molecules. Electro-osmotic flow of water through G4 pyrex sinter is linearly dependent on potential difference only up to ΔΦ = 70 volts. The results may be useful in designing suitable electrodialyzers for the purification of water. The electrophoretic velocity of glass particles in water has been found to vary linearly with applied potential difference up to ΔΦ = 160 volts. The results are also discussed in the light of the theory of thermodynamics of irreversible processes.